The present invention relates to a belt filter device for cleaning contaminated liquids, comprising an upper dirt chamber which receives the contaminated liquid, a clean chamber which is arranged underneath and receives the cleaned liquid, as well as a filter bottom which is arranged therebetween, is provided with a passage opening for the liquid and on which a revolving filter belt is arranged which can be moved along automatically as a function of the amount of contamination deposited on it, and with a cleaning device provided outside the dirt chamber which removes the contamination adhering to the filter belt.
This type of a belt filter device is known from European Patent Document EP-A 0 228 210 corresponding to U.S. Pat. No. 4,661,251, which is hereby incorporated by reference. This belt filter device operates according to the vacuum principle, with a revolving filter belt resting on the sieve bottom. Below this sieve bottom, a vacuum chamber is situated into which liquid is sucked through the filter belt. By means of the discontinuous conveying movement of the filter belt, the dirt deposited on the filter belt is conveyed via a delivery neck out of the tank for the liquid, and the dirt is removed by a filter belt cleaning device, such as a scraper or a blow-off device. Then the filter belt will travel through a washing station which washes off the residual dirt situated on the filter belt, this residual dirt being led back to the dirt chamber.
The filter belt used here is relatively large-meshed so that only dirt up to a certain grain size can be filtered out of the dirty liquid. However, when very fine dirt particles, such as grinding dust, and similar particles, must also be filtered out, a filter nonwoven must be used instead of the revolving filter belt. Such a nonwoven permits only one use and is disposed of together with the occurring dirt after the passage through the belt filter device. However, the disposal of this filter nonwoven requires high expenditures. In addition, a new roll of filter nonwovens must be inserted from time to time so that an additional monitoring is required. This type of a belt filter device is described, for example, in German Patent Document DE-GM 87 15 433. A disadvantage of such one-time filters is also the fact that a disposal presents problems.
Another disadvantage of belt filter devices comprising a washing station have been the high expenditures which were required for such a washing station. In order to achieve a sufficient cleaning and, at the same time, to ensure that the liquid which was required for the cleaning-off reached the dirt chamber, ducts for the liquid, a pump, covers and a housing had to be provided.